This invention relates generally to the alignment and fixation of bone segments as required for appropriate bone healing, for example after fracture or surgical intervention, and specifically to a device, and the tools needed to install the said device, for the alignment and fixation of cranial bone fragments.
In cases of bone fragmentation where bone fixation is desired, the appropriate alignment of the bone is also a desired result. This is especially true in the cranium, where bone fragmentation can occur as a result of trauma, congenital deformity, or of surgical intervention. In the field of neurosurgery, cranial bone fragments are frequently cut and removed to create defects to allow for access into the cranial cavity and the brain.
The bony cranium is generally regarded to have two surfaces: the outer surface which is characterized by the outer cortex of the bone and is adjacent to the scalp and soft tissue; and the inner surface which is characterized by the inner cortex of the bone and which is adjacent to the cranial cavity and the brain. Between the inner cortex and the outer cortex, which are dense layers of bone, lies the diploe which generally consists of soft bone and bone marrow. When a bone fragment is created, a cut between the bone fragment (the primary bone zone) and the remainder of the cranium (the secondary bone zone) is present.
Several methods of alignment and fixation of primary and secondary bone zones are known. Traditional techniques involve the use of several pieces of filament, such as wire, that are tied after being threaded through holes drilled obliquely through the outer cortex to the cut surface of both bone zones. Precise alignment of the two zones can be difficult and the technique can be cumbersome.
Commonly, the zones of bone can be aligned and fixated with a system of plates and screws (U.S. Pat. Nos.: 5,372,598; 5,413,577; and 5,578,036). A plate made of metal or other substance can be fixated to the outer cortex of the primary bone zone with screws whose penetration of the bone can be limited to the outer cortex. With three or more plates attached to the primary bone in such a way that the plates protrude beyond the edges of the primary bone zone, the primary bone zone can be introduced into a defect and aligned to the outer cortex of the secondary bone zone without danger of the primary bone zone falling too deeply into the defect in the secondary bone zone and exerting pressure on the underlying tissue such as the brain. Fixation can then be achieved by employing additional screws fixating the plates to the outer cortex of the secondary bone zone. Plates and screws systems allow for the alignment and fixation of the zones, while preventing the primary bone zone from falling below the level of the secondary bone zone without actually introducing a component of the device below the secondary bone zone. A plate with a spring clip extension has been described (U.S. Pat. No. 5,916,217). Plate and screw systems can be expensive and time consuming to use.
Devices that align the two bone zones by way of compressing them between the two disks positioned along the inner and outer cortex have been described. (Foreign Patents: DE 19603887C2, DE 19634699C1, DE 29812988U1, EP 0787466A1.) A pin connects the two disks aligning and securing two bone zones. These devices introduce foreign material that is left below the inner cortex, and they do not protect the underlying tissue from compression during the installation procedure.
Devices that fixate bone zones using friction forces created by a cam without a component that extends below the inner cortex are known and described (Patent DE 19634697C1). These devices also do not protect the brain from compression during the installation procedure.
Intramedulary pins are well known in the orthopedic fields for alignment of long bones. Such pins have also been described for cranial fixation (U.S. Pat. No. 5,501,685); however, the bone zones can not be aligned in three dimensions with this technique.
There is a need for an alignment and fixation device that is simple and rapid to use, versatile, and ultimately cost effective. There is also need for guidance of clip attachment to bone zones.
One object of the invention is to provide a device and instruments for its use and installation that aligns one cortex of a primary zone with one cortex of a secondary bone zone without extending to the opposing cortex, and which accurately fixates the bone zones to each other. When used in the field of neurosurgery, the device is applied to the primary bone zone and it aligns the outer cortex of the primary bone zone with the outer cortex of the secondary bone zone; it prevents the primary bone zone from entering the cranial cavity; and it provides fixation of the two bone zones. The alignment feature can be used independently from the fixation feature. An example of the use of the alignment feature is in the replacement of a cranial bone fragment which will be held in place by the tissue forces of the scalp, which allows for the bone fragment to be elevated away from the cranial cavity in cases where brain swelling occurs. Fixation can also be applied to attach the alignment device to the bone, using elements alone or in combination such as filaments, screws, rivets, pins, clips, cams, friction or adhesives. The alignment aspect of the invention can also be applied to situations where it is desired to offset the alignment of the bone fragment to the adjacent bone such as where the object is to create a more prominent chin by cutting the bone of the chin and advancing the bone fragment.
The fixation feature of the invention is likewise independent from the alignment feature. The fixation feature of the device relies on the principle that the device is fixated to the primary bone zone and the fixation feature grips the secondary bone zone by means of spring loaded tab or hook elements engaging the soft areas of the medullary space, irregularities along the cut surface, or a slot cut into the cut surface of the secondary bone zone.
The invention provides an improved clip meeting the above need or needs.
As will be seen, the preferred clip is configured to interconnect primary and secondary bone zones having edges spaced apart by a gap, the clip comprising
a) a tab such as a small plate to extend over and generally parallel to a surface of the secondary bone zone, and above a first level defined by that surface, and
b) a first projection carried by the tab and configured to penetrate the primary bone zone at the edge thereof, and below said surface level,
c) and an auxiliary tab associated with the first tab to be positioned to extend over a top surface of the primary bone zone to guide movement of the clip as the first projection penetrates the primary bone zone.
As will be seen, a second projection may be provided and carried by the tab and configured to engage the secondary bone zone at the edge thereof, and below said surface level, as well as below the level of the auxiliary tab.
It is another object to provide an extension of the tab projecting below said first level. That extension may carry the first projection, and may carry the second projection, if it is provided. In this regard, the second projection is typically located beneath the tab; and the first projection extends generally parallel to the tab and forwardly from a part of the tab extension below said surface level, and it preferably has a sharp terminal to enable penetration of diploe.
A further object is to provide the second projection to have a sharp terminal, and to extend at an angle toward the tab, in order to resist removal relative to the secondary bone zone.
Yet another object is to provide another second projection carried by the tab in sidewardly spaced relation to the first mentioned second projection, and configured to engage the secondary bone zone at the edge thereof, and below said surface level, as well as below the auxiliary tab.
An additional object is to provide a tab extension as referred to, but having S-shape or configuration, whereby enhanced spring support of one or both projections is realized; and also the S-shape of the extension facilitates its formation or manufacture.
An additional object is to provide a plate or flap defining the primary bone zone, and to provide multiple of the clips having their first projections penetrating the primary bone zone at different edges thereof, below a surface defined by the plate or flap.
The method of using the clip as referred to includes the steps
i) advancing the first projection to penetrate the primary bone zone,
ii) and locating the tab to extend over the surface of the secondary bone zone, and causing the auxiliary tab to guidingly engage and slide on the top surface of the primary bone zone during said penetration, and attaching the first tab to said surface.
As will be seen, the step i) preferably includes pushing the clip toward the primary bone zone to effect push-in penetration of the first projection into the primary bone zone. The method may further include providing a second projection carried by the tab and configured to engage the secondary bone zone at the edge thereof, and below its top surface level, the method including displacing the clip and said second projection to engage the secondary bone zone at the edge thereof, below said surface level. An additional step includes displacing the clip in a direction to effect scraping of the edge of the secondary bone zone by the second projection, the second projection oriented to resist reverse displacement of the clip in an upward or opposite direction relative to the secondary bone zone. In this regard, the method may include effecting penetration of the edge of the secondary bone zone by the second projection in an angular direction toward the tab. The bowed or S-shape of the extension provides enhanced spring effect to aid in effecting such penetration.
These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which: